This invention relates to combustion control apparatus for an internal combustion engine and particularly to such apparatus which includes means effective to detect the timing, relative to crankshaft rotational position, of peak combustion pressure in an LPP ignition timing control. Such apparatus uses a pressure sensing device, generally of the indirect type such as the engine headbolt combustion pressure sensor shown in the U.S. Pat. No. 4,491,010, to Brandt et al issued Jan. 1, 1985. This sensor senses combustion pressure within the combustion chamber through its flexing effect on the engine head relative to the engine block. However, such flexure is necessarily small in amplitude; and the signal produced by a piezoelectric element is likewise small in amplitude and susceptible to noise. This is especially true since the peak must be detected and the true peak may be difficult to distinguish amid high frequency noise peaks. Thus the sensor must be designed for maximum amplitude response and well shielded against electrical noise in the engine compartment of the vehicle.